Generally, high pressure high intensity discharge lamps include an arc tube disposed within a bulbous envelope. A gaseous electric relay device or glow starter device having a heat-responsive element adapted to emit electrons is shunted across the lamp. For example, U.S. Pat. No. 2,200,443, issued to Edward C. Dench, sets forth an appropriate glow starter device. Such a device develops a glow arc which heats a heat-responsive element and, in turn, causes a ballast to develop a potential across the discharge lamp whereupon conductivity of the lamp is effected. Thereupon, the glow starter device is rendered inoperative so long as lamp conductivity is maintained. However, it has been found that problems do exist in effecting proper operative of the glow starter device and lamp.
One attempt to rectify the above-described undesirable discharge lamp conditions is set forth in a copending U.S. application entitled, "Discharge Lamp With Integral Starter," filed Dec. 15, 1980, bearing U.S. Ser. No. 216,875 and assigned to the assignee of the present invention. Therein a gas-filled discharge lamp includes a glow starter device having a bimetal affixed to one contact and a rigid rod affixed to another contact. Short circuit current flows through the bimetal and rigid rod in an amount sufficient to activate the bimetal and separate the contacts. Thereupon, a pulse potential from a ballast sourse is applied to and normally effects conductivity of a discharge lamp. Should the lamp fail to ignite, the bimetal cools and returns to provide engagement of the contacts and a repetition of the cycle.
Another configuration for enhancing the previously-described relay system is described in a copending U.S. patent application, bearing U.S. Ser. No. 376,804, filed May 10, 1982, in the names of the present Applicants and assigned to the Assignee of the present application. Therein an arc tube is disposed within an evacuated envelope, a bimetal starter device having a bimetal and a rigid conductor each affixed to a switch contact are connected to leads passing through the evacuated envelope, and a spark gap is shunted across the arc tube. Upon occurrence of undesired excessive transient voltages, the spark gap serves to protect the discharge lamp and associated apparatus.
Although the above-described apparatus has numerous advantages over prior known structures, it has been found that there are some applications wherein a problem still exists. For example, it has been found that there are applications wherein the starter device has a tendency to stick or, in other words, the contacts of the starter device fail to open. Also, it has been found that lamps utilizing a starter device with a rigid contact member support tend to have a less than satisfactory life span. Moreover, lamps employing a starter with a rigid contact member appear to be more susceptible to shock which is obviously undesirable.